It depends what you want to do. Are you running a SE empire-wide? Do you have contact with overseas civs and lucrative trade routes? Are the other AIs in mercantilism? Are you running corporations? Do you want to deny AIs trade route access?

They are both powerful when used properly. Mercantilism also has the added bonus that it is available a bit earlier.

With mid/large sized cities and intercontinental trade, I'd say FM wins. But I feel it requires an inordinate investment for the return, and offers little to nothing earlier in the game.

Trade routes are a more extreme version of Cottage development, IMO, with the "more extreme" coming in the form of "no growth for a long, long time."

You would need to research trade routes to reach a more definitive conclusion. I know they're beneficial inversely with city size; small favors Merc, big FM. But obviously, if you can't land intercontinental (or trans-water) foreign trade routes with a long time ally, I'd say Mec is better.

Probably should have asked the question better, but in a situation where its a flat earth, no water whatsoever, will mercantilism come out ahead if all your cities are sitting around 12 - 14 pop, and late middle age tech levels.

Also, I think a lot of players fail to use Mercantilism properly, and ultimately base their opinion on which to run based on what effect it has on their net cash flow under each civic at their current slider settings.

If you have foreign trades routes available free market is pretty much always better. Even with representation it slaughters mercantilism the majority of the time. The only good time to use it is if everybody else is running it, or everybody hates you and you can't get open borders.

But this baseline assumes so much, and the ratio could actually go down to 3 +GPP : 1 ,
as having no open borders would only net you one more domestic trade route w/ Free Market. But trade routes are kind of tricky, they start at 1, they floor, and they have their host of multipliers. And you have to have alot of them; at Free Market, with +1 trade routes, you'd need as many foreign cities as you trade routes - three times as many foreign cities to hold the above ratio. With four trade routes per city you'd need 4x cities to have the above ratio. Often it is very hard to get open borders with 3 and 4 times as many cities as you own.

But the 4.25x can grow just as well. A harbor, etc, affects the trade routes and the population of foreign cities is a big factor. Foreign cities with pop 1 up to pop 10 have a 1x multiplier, but for each pop growth beyond that you get 10%. So, pop 11 gets a 1.1x multiplier, pop 12 gets a 1.2x multiplier and so on, up to pop twenty being double and pop 30 being triple. So the state of the world has a big affect. If all foreign cities were pop 20 the ratio would be 3 +GPP : 8.5

Well, if everyone is running mercantalism, there's little point not to yourself. Also, sometimes if you'd rather slow everyones tech rate down and/or you're very large, mercantilism is better. Or if you're running pacificism and trying to power to the next great person.

If you have foreign trades routes available free market is pretty much always better. Even with representation it slaughters mercantilism the majority of the time. The only good time to use it is if everybody else is running it, or everybody hates you and you can't get open borders.

No. Mercantilism could still rock in the late game pre-corps (Warlords and vanilla). 20+ cities with a free specialist each is very good. Post-corp, I'm not so sure.

If you have foreign trades routes available free market is pretty much always better. Even with representation it slaughters mercantilism the majority of the time. The only good time to use it is if everybody else is running it, or everybody hates you and you can't get open borders.

Building on this, I'd say merc is best when:

1. You're warring with minimal useful trade partners anyway. Might as well get something, then.
2. You have vassals. Merc allows trade with vassals, taking away one of its more crippling effects very quickly if you have any.
3. Isolation (obviously)

Generally I see it as a "warmonger game" civic, because while inferior to free market when there are trade routes, in games where you war a lot you usually don't have enough viable trade routes anyway, and if you do they're often vassals .

Hit F4 and look at the 'Info' Screen. Count up the total amount of you're receiving in trade from non-Vassals and make note of it. This is the 'benefit' of your foreign trade routes.

Then hit F1 and count the total number of cities you have. If not running Representation, multiply that number by 3. If you are or will be running Representation, multiply that number by 6. Make note of the result. This is the expected 'benefit' of Mercantilism [+Representation].

Compare the two numbers. In most cases, if the Merc value is comparable to or even slightly below the value, it's worth it to keep Free Market.

NOTE: If you're not running Free Market [or Mercantilism] when you do this calculation, count up the number of trade routes you have in your cities (not the commerce value ... just the number of how many you have). Add 1 to that number and then divide by the original number [of traderoutes] (i.e., num_traderoutes + 1 / num_traderoutes) ... the number should be greater than 1 (like 1.2 or something). You can then guesstimate the amount of increase to your trade routes by taking the total amount of from traderoutes including vassals (from the F4 Info screen) and multiplying it by the other number you just got. The result is usually close to the amount of increase you get from Free Market. (I hope that made sense...)